The invention pertains to conveyor belts which require electrical conductors, sensors, antennas, etc., embedded therein and systems which utilize such belts. More specifically this invention relates to an improved conductor, antennas, sensors, etc., which can be utilized in such belts.
Commonly an electrical conductor, such as a wire is formed into a closed current path, such as a loop and installed within an elastomeric conveyor belt. Brass plated high strength steel wire and copper cables (such as shown by British Patent No. 1,384,499) have been used. The belt may have one or more conductors extending the length of the belt, along the direction of travel, or it may have one or more conductors extending across the width of the belt spaced apart from one another along the length of the belt. These conductors remain substantially de-energized, i.e. no current flow, until they pass a detector, such as a coil which induces a current flow within the conductor. A detection means is then used to monitor or detect the induced current flow in the conductor. This information may be used to control the movement of the belt, such as positioning indication, or to indicate the occurrence of a rip or tear in the belt.
It is commonly known that heavy duty conveyor belts are susceptible to longitudinal slitting or tearing. If the belt is not stopped within a short period of time after the rip starts, the tear can continue along extremely long lengths of the belt causing extensive destruction or repairs of the belt and/or conveyor system. By stopping the belt quickly, the damage can be minimized, thereby reducing the cost and the down time to make repairs. Therefore, it is important to keep the integrity of the detection system high. However, over a period of time, one or more of the conductors may fail.
A conductor may fail for various reasons. A conductor within a belt is repeatedly flexed by the operation of the belt. This includes changes in direction, rollers, and by the load which is received, transported and discharged. This repeated flexing, bending, elongation, constriction etc., may result in the eventual failure due to fatigue of the conductor.
Another cause for failure is environmental. A conveyor belt may be subjected to a variety of environmental conditions. Water for example either as a liquid or a vapor, may come in contact with the conductor. The pulley covers in which these conductors are embedded may be subject to porosity and/or to the development of fine cracking or crazing during operation allowing for the entrance of moisture. The entrance of water can then corrode the conductor, causing it to weaken and eventually break. To compound this problem many belts are used in areas or environments having acidic (low PH) conditions. Therefore, the moisture which permeates through the belt to the conductor may also be acidic in nature. This increases the likelihood that the conductor will become corroded and eventually fail.
If a belt develops a rip, the rip will propagate until one of the conductors is broken. The detection system will then detect the broken conductor and stop the belt. However, if a conductor fails as described above, the detection system will stop the conveyor, not knowing that there really is not a rip. In order to continue operation, the conductor must be replaced, if possible, or the detection system adjusted to not monitor the area of the belt where the broken conductor exists or the entire detection system turned off. The latter two options result in reduced or no belt protection where rips could occur and cause much damage before detection.